1. Field of the Invention
The present invention relates to a solid state imaging device capable of automatic focus detection of a phase difference method and capturing parallax images for stereoscopy.
2. Description Related to the Prior Art
A solid state imaging device capable of automatic focus detection of a phase difference method (hereinafter referred to as the phase difference AF) in addition to imaging of a subject image is known (see Japanese Patent Laid-Open Publication No. 59-033409 and U.S. Pat. No. 6,829,008 corresponding to Japanese Patent Laid-Open Publication No. 2000-156823). The solid state imaging device for the phase difference AF has a plurality of phase difference detection pixels arranged in a predetermined pattern in an imaging surface. In each phase difference detection pixel, an optical axis of a microlens that condenses light into a photodiode (PD) and a center of an opening formed through a light shielding film covering the PD are shifted in a rightward or leftward direction. Thereby, the PD selectively receives the light from the rightward or leftward direction depending on the incident angle.
In the solid state imaging device of the phase difference AF, when a subject image formed on the imaging surface through an imaging optical system is out of focus, there is a positional shift between an image produced using the phase difference detection pixels which selectively receive the light from the rightward direction and an image produced using the phase difference detection pixels which selectively receive the light from the leftward direction. A defocusing amount of the imaging optical system is obtained from an amount of the positional shift, and the imaging optical system is moved accordingly. Thus, the phase difference AF is performed.
Recently, a solid state imaging device having only the phase difference detection pixels arranged in the imaging surface has been suggested. In the solid state imaging device, a right-eye image (R viewpoint image) is produced using the phase difference detection pixels which selectively receive the light from the rightward direction. A left-eye image (L viewpoint image) is produced using the phase difference detection pixels which selectively receive the light from the leftward direction. Thereby, a pair of R and L viewpoint images (hereinafter referred to as the parallax images) causing binocular parallax are obtained. Generally, to capture the parallax images, two pairs of taking lenses and solid state imaging devices are disposed parallel with each other. The above-configured solid state imaging device, on the other hand, only needs a pair of taking lens and solid state imaging device. Thus, the parallax images are captured with a simple configuration.
When the phase difference detection pixel is formed by shifting the opening of the light shielding film, the size of the opening needs to be reduced in accordance with the amount of the shift. Hence, the sensitivity of the phase difference detection pixel is reduced as compared with that of a normal pixel in which the optical axis of the microlens is coincident with the center of the opening of the light shielding film. There is another type of the phase difference detection pixel in which the optical axis of the microlens is shifted relative to the center of the light receiving surface of the PD. In this case, a diameter of the microlens is reduced so as to prevent the light from being incident on the adjacent pixel. This configuration also reduces the sensitivity of the phase difference detection pixel. It is thus necessary to improve the sensitivities of the phase difference detection pixels in the solid state imaging device.